As lithographic printing plate precursors, those comprising a hydrophilic support having provided thereon a lipophilic photosensitive resin layer have hither to been widely used. As the plate-making methods, methods of obtaining desired printing plates by mask exposure (open-frame-exposure) via a lith film and then dissolving and removing the non-image area are ordinarily used.
Digitized techniques of electronically processing, accumulating and outputting image data using a computer have prevailed in recent years, and various image output systems corresponding to these digitized techniques have been put to practical use. As a result, a computer-to-plate (CTP) technique of directly making a printing plate by scanning digitized image data without using a lith film with highly convergent light such as a laser beam is eagerly desired. With such a tendency, it has become an important technical subject to obtain a printing plate precursor well adapted to such a purpose.
As such a lithographic printing plate precursor capable of scanning exposure, a lithographic printing plate precursor having a constitution comprising a hydrophilic support having provided thereon a lipophilic photosensitive resin layer (hereinafter sometimes referred to as “a photosensitive layer”) containing a photosensitive compound capable of generating an active species, such as a radical and a Bronsted acid, by laser exposure has so far been proposed and printing plate precursors of these kinds have been now on the market. A negative lithographic printing plate can be obtained by scanning exposing the lithographic printing plate precursor with laser beams on the basis of digital data to generate an active species, causing physical or chemical changes in the photosensitive layer by the action of the active species to make the photosensitive layer insoluble, and then development processing the lithographic printing plate precursor.
As a negative lithographic printing plate precursor, there is known a negative lithographic printing plate precursor comprising a hydrophilic support having provided thereon a photopolymerization type photosensitive layer containing a high speed photopolymerization initiator, an addition polymerizable ethylenically unsaturated compound, and a binder polymer soluble in an alkali developing solution, and, if desired, an oxygen-shielding protective layer (e.g., refer to patent literature 1). Lithographic printing plate precursors of such type have desired printing properties, e.g., excellent in productivity and, further, easy to perform a development process, excellent in resolving power and ink receptivity.
As the binder polymer, alkali developable organic polymers, e.g., a methacrylic acid copolymer, an acrylic acid copolymer, an itaconic acid copolymer, a crotonic acid copolymer, a maleic acid copolymer, and a partially esterified maleic acid copolymer are used (e.g., refer to patent literatures 2 to 9).
In addition, for improving a film coating property, aging stability and press life, it is disclosed to use a polyurethane resin having an allyl group as the binder polymer in a photosensitive layer (e.g., refer to patent literature 10). However, a photosensitive composition capable of high sensitivity recording and satisfying all of storage stability (storage stability before exposure) and a film-forming property has not been obtained yet. Accordingly, as the present state, a negative lithographic printing plate precursor capable of high sensitivity recording with infrared laser beams and excellent in storage stability (storage stability before exposure) and press life has not been obtained yet.
[Patent Literature 1]
JP-A-10-195119 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”.)
[Patent Literature 2]
JP-A-59-44615
[Patent Literature 3]
JP-B-54-34327 (The term “JP-B” as used herein means an “examined Japanese patent publication”.)
[Patent Literature 4]
JP-B-58-12577
[Patent Literature 5]
JP-B-54-25957
[Patent Literature 6]
JP-A-54-92723
[Patent Literature 7]
JP-A-59-53836
[Patent Literature 8]
JP-A-59-71048
[Patent Literature 9]
JF-A-2002-40652
[Patent Literature 10]
Japanese Patent No. 2712564